A variety of methods have been developed to detect target biomolecules, like deoxyribonucleic acids (DNA), in a sample. Among these methods, a nanopore method has been spotlighted in conjunction with a high-sensitivity DNA detection system. A variety of DNA detection systems using nanopores have been published to date. For example, a base sequence of DNA may be determined or it may be determined whether DNA is single stranded or double stranded by detecting a slight change in a current that occurs when DNA translocates through a nanopore.
Such DNA detection systems using nanopores enable DNA to translocate through a fine nanopore formed through a thin layer by moving DNA toward the fine nanopore according to an electrophoresis phenomenon. For example, if a sample liquid solution including DNA is filled in a front end of the nanopore, and voltages are applied to the front and rear of the nanopore, DNA having negative charge moves toward an anode. Thus, DNA may translocate through the nanopore by placing a cathode in the sample liquid solution in the front of the nanopore and the anode in a reservoir in the rear of the nanopore.
However, although a strong electrolyte having good ion conductivity is used as a liquid solution, since an ion translocation area is rapidly reduced in the nanopore, resistance greatly increases, which causes a voltage drop near the nanopore. As a result, an electric field formed between the anode and the cathode is mainly distributed near the nanopore. Thus, DNA are merely spread by a thermal motion in the sample liquid solution in the front end of the nanopore having a weak electric field, and then are induced to the nanopore if the DNA reach a limited region near the nanopore in which the electric field having an intensity that is higher than a predetermined level is distributed.